Combine the prosciutto, onion, carrots and celery on a cutting board and chop into very small pieces.

In a large frying pan, melt butter over medium heat. Add prosciutto mixture and sauté, stirring often, for 10 minutes or until lightly browned. Transfer to a heavy, large saucepan.

In same frying pan, heat olive oil and lightly brown beef and pork over medium heat, stirring constantly to break up any lumps. Pour in the wine, increasing the heat. Boil briskly, still stirring constantly, until almost all of the liquid has evaporated. Add meat mixture to prosciutto mixture in saucepan. Stir in the stock and tomato purée. Bring all to a boil over high heat, then reduce the heat and simmer, partially covered, for 45 minutes, stirring occasionally.

Meanwhile, melt remaining 2 tablespoons of butter over high heat in the original frying pan. Add chicken livers and sauté for 3 to 4 minutes, or until firm and lightly browned. Remove livers from frying pan and dice. Set aside and add to sauce 10 minutes before it is done.

A few minutes before serving, stir in the cream and let it heat through. Season sauce with nutmeg, salt and pepper to taste.